This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-206924, Jul. 6, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a semiconductor device having a junction-termination structure of a RESURF (RESURF: REduced SURface Field) type, and particularly to an improvement of the junction-termination region of a semiconductor chip.
2. Description of the Related Art
FIG. 4A is a sectional view schematically showing the junction-termination region and its vicinity of a conventional punch-through type IGBT (Insulated Gate Bipolar Transistor) chip having a junction-termination structure of a RESURF type. As shown in FIG. 4A, the IGBT chip has an active region R11, a junction-termination region R13 located around the active region R11, and a separation region R12 interposed between the active region R11 and the junction-termination region R13. An Nxe2x88x92-first base layer 62, an N+-buffer layer 68, and a P+-collector layer 70 are disposed entirely over these regions R11 to R13. In the active region R11, P+-second base layers 64 are formed in the surface of the first base layer 62, and N+-emitter layers 66 are formed in the surface of the second base layers 64.
A gate electrode 74 is disposed on and faces, through a gate insulating film 72, the portion of each second base layer 64 sandwiched between the first base layer 62 and the corresponding emitter layer 66. An emitter electrode 76 is disposed in contact with the second base layers 64 and the emitter layers 66. A collector electrode 78 is disposed in contact with the collector layer 70.
A P+-first diffusion layer 82 is formed in the front surface of the first base layer 62, and extends from the active region R11 through the separation region R12 into the junction-termination region R13. In the junction-termination region R13, a Pxe2x88x92xe2x88x92-second diffusion layer 84 for relaxing the surface electric field is formed in the front surface of the first base layer 62. In the active region R11, a contact electrode 90 is disposed in contact with the first diffusion layer 82. The contact electrode 90 is electrically connected to the emitter electrode 76.
According to research conducted by the present inventors, it has been found in the structure shown in FIG. 4A, that there are ill effects of a parasitic current flowing in the junction-termination region, as described later.
According to a first aspect of the present invention, there is provided a semiconductor device including an active region where a main semiconductor device section is disposed, and a junction-termination region located around the active region, the device comprising:
a first semiconductor layer of a first conductivity type, disposed as a semiconductor active layer common to the active region and the junction-termination region;
a first diffusion layer of a second conductivity type formed in a surface of the first semiconductor layer, and extending from the active region into the junction-termination region;
a second diffusion layer of the second conductivity type formed in a surface of the first semiconductor layer and in contact with the first diffusion layer, the second diffusion layer extending in the junction-termination region, and having a carrier impurity concentration lower than that of the first diffusion layer;
a first contact electrode disposed in the active region and in contact with the first diffusion layer, and electrically connected to a first main electrode of the main semiconductor device section;
a second contact electrode disposed in the junction-termination region and in contact with the first diffusion layer, and surrounding the active region; and
a connection electrode electrically connecting the first and second contact electrodes to each other.
According to a second aspect of the present invention, there is provided a semiconductor device including an active region, a junction-termination region located around the active region, and an intermediate region interposed between the active region and the junction-termination region, the device comprising:
a first semiconductor layer of a first conductivity type, disposed as a semiconductor active layer common to the active region, the intermediate region, and the junction-termination region;
a second semiconductor layer of a second conductivity type formed in one surface of the first semiconductor layer in the active region;
a third semiconductor layer of the first conductivity type formed in a surface of the second semiconductor layer;
a fourth semiconductor layer disposed on or in another surface of the first semiconductor layer in the active region;
a gate electrode facing, thorough a gate insulating film, a portion of the second semiconductor layer sandwiched between the first semiconductor layer and the third semiconductor layer;
a first main electrode disposed in contact with the second semiconductor layer and the third semiconductor layer;
a second main electrode disposed in contact with the fourth semiconductor layer;
a first diffusion layer of a second conductivity type formed in a surface of the first semiconductor layer on the same side as the second semiconductor layer, and extending from the active region through the intermediate region into the junction-termination region, the second semiconductor layer and the first diffusion layer having substantially the same carrier impurity concentration;
a second diffusion layer of the second conductivity type formed in a surface of the first semiconductor layer and in contact with the first diffusion layer, the second diffusion layer extending in the junction-termination region, and having a carrier impurity concentration lower than that of the first diffusion layer;
a first contact electrode disposed in the active region and in contact with the first diffusion layer, and electrically connected to the first main electrode;
a second contact electrode disposed in the junction-termination region and in contact with the first diffusion layer, and surrounding the active region; and
a connection electrode disposed in the intermediate region, and electrically connecting the first and second contact electrodes to each other.